Layer Methodology
Impervious Surface
A derived built-surface index that translates roads and buildings into permeability pressure.
Map Role
A derived estimate of built-surface intensity across dissemination areas.
What It Shows
This layer estimates how much of each dissemination area is likely covered by impervious surfaces. It is designed as a planning proxy for runoff, heat retention, and planting constraints.
Sources
- Road Network ETL output
- Building footprints when available
- Census dissemination areas from the equity layer
Method
- 1.Use dissemination areas as the base geography.
- 2.Estimate road surface area by buffering road segments with a width derived from lane counts.
- 3.Add building-footprint area where that source is available.
- 4.Divide total estimated impervious area by dissemination-area size and classify the result from very low to very high.
Refresh Cadence
Derived snapshot. Refresh when roads, buildings, or census geometry are updated.
Coverage
Six-city dissemination areas scored with estimated impervious percentage.
Key Fields
impervious_pct
Estimated share of the dissemination area covered by impervious surface
impervious_class
Class from very low to very high imperviousness
road_area_m2
Estimated impervious road area inside the dissemination area
building_area_m2
Estimated or measured building area inside the dissemination area
Caveats
- This is a proxy layer, not a directly measured impervious raster.
- Where building footprints are absent, the estimate can understate built coverage.
- Road widths are generalized from lane counts and should be treated as approximate.